Corrosion in Steels – Its Types and Testing Corrosion is a universal natural process. The effect of corrosion is seen in every-day life in the form of rusted steel parts. Corrosion has a huge economic impact. About a fifth of the global annual steel production goes towards simply replacing steel parts damaged by corrosion. Even though it involves higher up-front cost, correct and efficient corrosion protection at the source helps save money and resources in the long run. Failure due to corrosion can result into dramatic consequences. Corrosion is the gradual degradation of a metal by chemical, often electrochemical reaction with the surrounding environment. Corrosion results into loss of material properties such as mechanical strength, appearance, and impermeability to liquids and gases. Whether steel is corrosion resistant in a specific environment depends on the combination of the chemical composition of steel and the aggressiveness of the environment. As per ISO 8044:2010, corrosion is the physicochemical interaction between a metal and its environment, which results in changes in the metal’s properties and which may lead to significant functional impairment of the metal, the environment, or the technical system of which they form a part. Corrosion takes place when there is a change in the steel’s or system’s properties which may lead to an undesirable outcome. This can range simply from visual impairment to complete failure of technical systems which cause great economic damage and even present a hazard to the people. The typical corrosion process can be regarded as the thermodynamically favoured reverse reaction of the metal-winning (extraction) process (Fig 1). Like all chemical reactions, corrosion processes take place when conditions favour the related chemical reactions (thermodynamics). Then, potential other factors drive the speed of the reaction (kinetics). Fig 1 Chemical reactions of iron during...